Cellular communication systems are well known, and are evolving to meet higher communication capacity requirements as more people are adopting cellular communication system for their everyday communication needs. For example, one communication system, which has evolved from a communication system operating according to the well-known IS-95A standard, is commonly referred to as the CDMA 2000communication system. The IS-95A and CDMA 2000 communication systems operate according to their transmission technologies defined by respectively IS-95A and CDMA2000 standards. The IS-95A and CDMA2000 systems are compatible systems. Other systems compatible with one or more of the existing systems, such as Wide Band CDMA (WCDMA) system, are also being proposed and implemented. Such compatible communication systems are being proposed or implemented at the time of filing this application. Therefore, the extend of the systems compatibility may change in future without departing from the basic compatibility requirements. In the CDMA 2000 communication system, for example, layer 2 and above messaging/signaling can be compatible with the IS-95A communication system; however, the air-interface may be different between the communication systems. Therefore, the two systems have compatible radio transmission technologies even though they have differences in operation.
The systems that are based on IS-95A transmission technology are older systems and have been implemented and in use in many regions of the world. The CDMA 2000 and WCDMA system are new systems. Such new systems are implemented in an overlay fashion in the areas covered by the older and compatible systems. As such, the capacity of the system consisted of the older and new systems is increased which allows more people to communicate via the cellular technology in the same area. A mobile unit compatible with both systems may communicate via radio transmission technology of either system. The base stations of the compatible systems provide the wireless and wireline landbased connections. Such base stations may be co-located or in proximity of each other. To a user of the system, the base stations appear as a single base station having compatible radio transmission technologies. It may be transparent to the user as to which technology is being used by her mobile station while in operation.
There may be three types of mobile stations. The first type communicates only according to the older transmission technology, the second type according to the new transmission technology, and the third type according to the old or the new type of transmission technology. The third type is commonly referred to as a dual mode mobile station. The dual mode mobile station may be capable of hand-off between the transmission technologies while a call is in progress with the base station. In case there are three compatible systems in a geographic area, a mobile station may be of tri-mode, which can operate in any of the three systems; as a result, there may be more than three types of mobile stations. A method and apparatus for implementing diversity for a dual-mode communication unit are described in an application for a patent by Ten-Brook et al, having at least one common inventor with the present application, App. No. 09/111,974,filed on Jul. 8, 1998, in the United States Patent Office, and assigned to the assignee of the present application, incorporated by reference herein.
The base station, normally, has limited radio link capacity of each of the compatible radio transmission technologies. The radio link capacity may be limited by either the amplifier maximum linear gain, which is amplifying the composite signal, or the number of channel elements that provide resources for the radio links in the system or both the amplifier and channel elements. For example, when the radio link capacity of the older transmission technology reaches near its limit, the base station may refuse communication service to a mobile station that works only according to the older transmission technology, similarly, base station may refuse service to a mobile station that works only according to the new transmission technology if the radio link capacity of the new technology reaches near its limit. The dual mode mobile stations that work in both types of technologies may receive communication service as long the base station has a radio link capacity available in either one of the radio transmission technologies.
There is no independent control of the number of mobile stations roaming into and out of the coverage area. Furthermore, there is no independent control of the ratios of the old, new and dual mode mobile stations present in a coverage area. As a result, there may be a situation that the base station has an available radio link capacity, for example, in the new transmission technology while the available capacity in the older technology is being used to its limit by the older type mobile stations and dual mode mobile stations using the older type transmission. The exhaustion of the radio link capacity of the older type transmission technology, when effecting the dual mode mobile stations, may be solved simply by handing off some of the dual mode mobile stations from the old to the new transmission technology; however, there is no independent control of balancing availability of radio link capacity of the old and new transmission technologies for all types of mobile stations when both transmission technologies are made available in a coverage area.
Therefore, there is a need for a method and apparatus for controlling capacity and communication traffic in such wireless communication systems.